Why is my phone showing 1 message and there are no messages in my phone?

If it turns out that there is no message using lobsterghost1’s instructions, try this.

Force close the messages app and then restart your phone and see if the message notification goes away.

To force close the app, swipe up,from the bottom of the screen to get to the app switcher. Find the messages app preview and swipe it up and off the screen to close it.

To power the phone down go to Settings>General>Shut down. To power up, hold the sleep/wake button until you see the Apple logo on the screen.

Open the Messages App. Tap Edit. If there is an unread message, you'll see Unread Messages there.

What also works is having Siri read all unread messages.